The present invention relates to a hollow electrode plasma excitation source and particularly to such a source wherein the hollow electrode comprises an anode having a relatively positive voltage supplied thereto, and within which is received a centrally disposed cathode.
Systems are known for atomic emission spectrometry wherein graphite furnace vaporization is combined with a glow discharge. The furnace vaporizes a substance which is to be analyzed, and the glow discharge generates excited states of atoms in the vapor so that their emissions can be measured. Thus, a polychromator used to view the glow discharge can be employed for analysis of the vaporized substance. According to the known system, a tubular graphite furnace is used for sample vaporization, and also as the glow discharge cathode. An electrode external to the end of the furnace serves as the anode for the glow discharge. The glow discharge in the furnace cathode comprises the source of radiation which is analyzed.
Unfortunately the prior art apparatus has experienced problems relative to stability and range of stability of the plasma, as well as reproducibility of analysis. Also, electric fields between the furnace and the vacuum housing for the furnace require shielding considerations.